Investment in renewable energy isn't limited to solar and wind developers. Some of the biggest companies in the world are investing heavily in renewable energy. For example, according to the Solar Energy Industries Association, Apple, Amazon, and Walmart are the biggest solar energy investors in the U.S., and commercial customers are responsible for 8,350 megawatts (MW) of solar installations in the U.S. And that's just corporate investment in solar, a portion of the renewable energy industry.

I've highlighted that a number of big companies are betting on renewable energy, but what are the companies that would surprise you with their level of investment? Three of our Motley Fool contributors think Total (NYSE:TTE), Cummins (NYSE:CMI), and Phillips 66 (NYSE:PSX) are secretly renewable energy stocks in the making. 

Wind and solar assets with a city skyline in the background.

Image source: Getty Images.

Big oil is betting big on renewable energy

Travis Hoium (Total): Big oil companies are going to have a hard time making the transition to renewable energy simply because of the momentum they have in fossil fuels. One company with a decent shot at making the transition is Total, the French oil giant, which has made billions in investments into renewables over the course of the last decade. 

Total owns a controlling interest in SunPower (NASDAQ:SPWR) and Maxeon Solar Technologies (NASDAQ:MAXN), industry leaders in distributed solar development and solar manufacturing respectively. It also owns Saft, a battery technology company that's developing utility-scale battery projects. On top of those investments, Total owns at least 5 gigawatts (GW) of renewable energy assets and has ambitions to develop 35 GW by 2025. 

What Total has done is take an economic interest in the technology companies and then use its scale and industry connections to build renewable energy developments around the world. Renewables are still a small percentage of the company's business, but the investment will grow in the next decade, and Total is set up to make the renewable energy transition better than almost any other oil company. That's a surprising position for a company that's considered a big oil stock by most investors. 

The most basic element

Howard Smith (Cummins): If a large company has five business segments, and one of them represents less than 1% of net sales, you probably wouldn't expect an entire investor day dedicated to it. But that's what Cummins did last month with its Hydrogen Day presentation. 

While still off a very low base, Cummins' New Power segment doubled revenue in the third quarter versus the prior year period, and the company spent Nov. 16 updating investors on its plans for fuel cell and hydrogen technologies. The entire segment had $18 million in sales for the recently reported third quarter, but Cummins expects at least $400 million in just sales of electrolyzers -- which are used to generate hydrogen for fuel cells -- in 2025. 

h2 fuel symbol on a large, metal structure.

Image source: Getty Images.

Cummins also said it will have 100 trains powered by its fuel cell systems by 2025. The company is focusing on two areas of hydrogen use as it helps the world transition to a low carbon future. Industries including steelmaking already use hydrogen in processing, but Cummins believes it can replace the less environmentally friendly production of hydrogen with green hydrogen using its electrolyzer technology. And Cummins plans to participate as fuel cell-powered electric vehicle demand is growing in the heavy-duty truck, bus, and train markets. 

"As the world transitions to a low carbon future, Cummins has the financial strength to invest in hydrogen and battery technologies," Cummins chairman and CEO Tim Linebarger said in the presentation. Cummins won't be abandoning diesel and natural gas powertrains completely, but investors who want to participate in the transition to renewable energy can ride along with Cummins as it bets more of its market goes that direction. 

This old oil dog is learning new tricks

Jason Hall (Phillips 66): Best known for its oil refining and marketing businesses, Phillips 66 is indeed heavily invested in the continued use of hydrocarbons for transportation. But what may not be as well known is the company's more recent focus on renewables.

In 2018, the company began refining renewable diesel from waste oil at its Humber, U.K., refinery and plans to increase the output to 3,000 barrels per day in January. For the uninitiated, that's almost 46 million gallons of renewable diesel per year that will replace diesel made from crude oil

But that's just the beginning. Phillips 66 has big renewable plans for its Rodeo refinery in Northern California, which it plans to convert to 100% biofuels. Rodeo Renewed, as it has been dubbed, is aimed at boosting the company's total renewable diesel production to 340 million gallons per year. 

So while Phillips 66 will indeed continue to rely on fossil fuels for many years to come, management has already begun taking action to align the company's future with the transition to renewable fuels. 

Making the energy transition

Total, Cummins, and Phillips 66 may not be companies you think of as renewable energy giants, but they're making big investments in the industry and have the balance sheets to make bets that smaller companies can't. They may still have fossil fuels at their core, but their futures could all be in renewable energy. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.